1. Field of the Invention
This invention relates generally to ducting as used in air conditioning systems, and more particularly to a duct fitting for interconnecting such ducting.
2. Description of the Prior Art
It is customary in the heating, cooling and ventilating field to use a main, or trunk duct, having extending from it one or more branch ducts. Various fittings have been proposed for connecting a branch duct to an associated main duct. One manner of attaching a fitting to a duct is shown in U.S. Pat. No. 3,290,066 issued Dec. 6, 1966 to T. Primich et al wherein a plurality of tabs formed so as to extend axially from the fitting are bent over in order to secure a fitting on an associated duct. A significant problem, however, with regard to time, tools and the relatively high degree of skill required to accurately cut a properly sized hole in the trunk duct, which may be constructed from a rigid or flexible material, such as reinforced fiberglass and the like, prior to insertion and attachment of the branch duct fitting.
U.S. Pat. No. 3,349,792 issued Oct. 31, 1967 to M. E. Larkin, and U.S. Pat. No. 3,609,056 issued Sept. 28, 1971 to E. D. Hougen, disclose examples of hole cutting tools which can be used for cutting holes in air conditioning ducting. A basic disadvantage of this approach, however, is that a large number of cutting tools of various sizes must be kept available in order to cut a hole which is sized properly for a specific duct fitting. Further, there can be difficulty in inserting a fitting into a hole cut for it, if the pre-cut hole is irregular, or too small, and if the hole is too large, the fitting will be loose and most likely it will be a source of undesirable air leakage.
Another problem encountered with the installation of branch duct fittings to main ducts of air conditioning systems, and the like, is that there must be found a manner of attaching the fitting to the duct. Other than the use of the aforementioned bent tabs, it is a common practice to employ bolts and similar fasteners which result in projection of the ends of the fasteners into the main duct. Such projections are generally undesirable, inasmuch as they cause turbulence in the air stream within the duct.
Accordingly, it has been proposed to provide quick connection arrangements on duct fittings in order to eliminate the attachment problems referred to above, as well as to insure a good fit between the fitting and an associated duct. Examples of such quick connections can be found in U.S. Pat. No. 3,477,745 issued Nov. 11, 1969 to J. W. Williams et al, and U.S. Pat. No. 3,915,477 issued Oct. 28, 1975 to D. R. Timmons. These fittings are intended specifically for use with reinforced fiberglass ducts and employ helical rings formed about the periphery of the connection end of the fitting which permit the connection end of the fitting to be threaded through a pre-cut hole. Once threaded through the duct, the split ring or flange retains the fitting in place on the duct.
With the above approach, however, not only is it first necessary to pre-cut a hole in the associated duct, the problems of which are discussed above, but during insertion of the fitting into the hole, the helical rings tend to tear or shred the wall in the area circumscribing the hole. This also is the case with U.S. Pat. No. 3,726,545 issued Apr. 10, 1973 to J. R. Grim et al which discloses an air duct connector especially for use with reinforced fiberglass ducts in which the leading edge of the connector is provided with widely spaced cutting teeth for initially forming a circular aperture in the duct wall. Widely spaced radially extending tabs are provided proximate the cutting teeth for being threaded into the hole during cutting thereof to lock the fitting in the hole in the trunk duct wall. Besides tearing, or shredding the wall, a disadvantage of this construction is that the cutting teeth which are not intended to be bent over, will extend into the fluid flow path of the trunk duct so as to cause turbulence therein. Further, in order to remove the cutout portion, or slug, of the duct wall from the interior of the duct, which can cause turbulence, air flow restriction, noise, and the like, if left in the duct, it must be removed carefully through the mounting fitting in order to avoid the projecting cutting teeth.
Poorly fashioned cuts such as the pre-cutting of holes by free hand use of a knife, razor blade, and the like, as required in some of the hereinbefore described prior art fittings, usually results in loose fits and air leakage. Also, sidewall tearing or shredding resulting from the use of other above discussed prior art fittings, can result in leakage prone weak spots in the areas where the fittings are mounted to the trunk duct. In addition, shredded fibers must be kept out of the air moving in the duct system to prevent the known health hazard associated with airborne fibers.
Regardless of the technique used to mount a branch line fitting in a main, or trunk duct, a problem has long existed with regard to diverting air out of the air flow stream in the trunk duct into the branch duct. In many prior art systems, this air diversion problem is simply ignored with the result being that air pressure in the trunk duct will be totally relied upon to cause some air to move into the branch duct. In most instances, this results in inadequate air flow in the branch lines.
In my prior co-pending U.S. patent application, Ser. No. 383,558, filed June 1, 1982 for a Self-Tapping Duct Fitting, I attempted to solve the air diversion problem by pivotably mounting a flat plate damper in the duct fitting and providing a suitable linkage so that subsequent to fitting installation, the damper could be moved to a fully open position wherein a relatively small portion of the flat plate extended from the fitting into the air stream of the trunk duct. While this improved the situation with regard to the air diversion problem discussed above, the air striking the flat plate damper created considerable turbulence both in the trunk duct and in the branch duct, and acted as a restriction in those air streams. In addition, the relatively expensive damper, and its mounting arrangement, and linkage were far too costly for the minimal results achieved therefrom.
Therefore, a need exists for a new and improved duct fitting and method for mounting thereof which overcomes some of the problems and shortcomings of the prior art.